The present invention relates generally to a switch for a light pipe, and more specifically to a coaxial electrophoretic device for modulating the intensity of light travelling through a light pipe.
In the operation of light pipes it is often desirable to control the intensity of the light discharge lamps as the light source for light distribution, it is desirable to control the light in the light pipe without modulating the light source. Several methods have been used in the past to control the modulation of the light through the light pipe.
One such method known in the art is controlling a mechanical shutter placed in a gap between two portions of a light pipe. In one position, the shutter blocks the transfer of light from one light pipe to the next; and in another position light is free to pass from one light pipe to the next. One difficulty has been that, due to index of refraction changes as the light travels from the light pipe to air and back into the light pipe, reflections at the light pipe/air interface cause a reduction light intensity. Furthermore the moving mechanical shutter has reliability problems.
Another method used for modulating light is known as the Kerr effect as shown in U.S. Pat. No. 3,442,568, The apparatus has a center electrode which has a cladding of high refractive index glass covered in turn by a Kerr effect material. When the electrode is charged the refractive index of the Kerr effect material changes, causing light to be absorbed into the material and reducing the light transmitted through the glass. One problem with such an apparatus is that having an electrode in the center of the light pipe is not practical in many application.